1. Field of the Invention
The invention relates to a screen basket having a plurality of rods each positioned approximately parallel to the rotational symmetrical axis of said basket and having a plurality of rings connecting said plurality of rods with said plurality of rods forming screen slots therebetween and a method for its manufacture. Such a screen basket is known from DE-OS 33 27 422.
Since screen baskets with milled slots have the disadvantages of high labour cost caused by the milling itself and the remachining of the sharp edges resulting from milling, an attempt has been made, by welding on supporting elements, to manufacture such screen baskets with slots, which may be very fine, down to 0.15 mm slot width. For this purpose, rods with a rectangular cross-section have been favoured. The screens have a high efficiency per se, but it is very difficult to make the small gap widths with suitable accuracy and uniformity. Furthermore, there is also the great disadvantage that these screen baskets display only a low strength because of the generally only small triangular cross-sectional surface and because of the small permanently welded cross-section.
To be able to manufacture these screen baskets economically, the course adopted so far has been either to produce a flat wire mat which was later bent into the round, rotationally symmetrical shape of the screen basket, or, contrary to the final, later shape of the screen basket, the triangular rods have been wound up on a kind of lathe with a cylinder spirally onto parallel retaining rods. After having cut open this contrary screen basket--which has slots running practically in the peripheral direction--this screen basket mat has been stretched and then shaped into a screen basket in the opposite direction, on which the slots then run parallel to the axis of rotational symmetry between the triangular profile rods. These working methods lead to major sources of error in accuracy of the widths of the screen slots and also in respect of the given strength. Furthermore, after bending, supporting rings also had to be welded to the retaining elements of the profile rods to create the necessary strength for the screen basket. Despite this great deal of labour, however, there is the disadvantage of a not completely uniform gap width, which means that the efficiency of these screen baskets is relatively poor.